The present invention relates to a control apparatus for controlling an electric vehicle, and in particular, it relates to a control apparatus for controlling power devices in a power converter which supplies power to an ac motor for driving the electric vehicle in which the power devices are driven by a digital actuating signal.
Many of the prior art control apparatuses for driving an ac motor, whether an induction motor or a synchronous motor which uses permanent magnets, in practice utilize the vector control method which divides a motor current into a torque current Iq and an exciting current Id in order to control the motor. Various control methods utilizing the vector control method have been proposed for the purpose of improving static and dynamic characteristic control performances and the like. For example, in JP-A-6-178575, timing control between an exciting current reference and a torque current reference is disclosed for improving such control characteristics.
For a drive unit including a motor and a power converter for driving an electric vehicle, it is essential that it be compact in size and light-weight in order to satisfy the requirement of improving the mileage per charge of a battery. In order to satisfy such a requirement for compactness and light-weight, it becomes necessary to increase its motor speed, for example, over several thousand revolutions per minute as well as frequencies of its power converter, for example, over several hundred Hz. As disclosed in the above-mentioned prior art JP-A-6-178575, it is a general practice to compute reference values of the torque current and exciting current using a microcomputer for motor current control in a control unit which produces a drive signal to drive power devices in the power converter which supplies power to the ac motor. However, since a number of electronic components are required such as logic circuits, operation amplifiers and the like, in addition to the microcomputer, increases in size and weight of the control unit cannot be avoided according to the prior art, thereby preventing realization of the requirements for compactness and light-weight of the drive unit.